An A-list cast, a script dotted with witty one-liners, a funny idea.it must have looked like a money-spinner on paper. Diane Keaton is mad mum Marilyn, who puts the "S" in front of mother. It's Halloween, and she's dressed as a giant pumpkin. She accuses her husband of infidelity, and walks out on him and into her son's home - bags, pumpkin suit and pack of dogs in tow. "She will bring great unhappiness to our household," says long-suffering son Noah (comic actor Dax Shepard from Punk'd, Idiocracy and Zathura) to wife Clare (Liv Tyler). Add another unwelcome houseguest in Clare's wannabe screenwriter cousin (played by real life screenwriter/actor Mike White, School Of Rock), and the ingredients for comedic chaos are in place. So far, so good. But thirty minutes into Smother, when mother and son take on jobs at the same carpet store, it unravels into silliness.

This flick from writer/director Vince Di Meglio (the co-writer of License To Wed) does generate laughs - just not as many as intended. Some scenes, like the physical fight between Noah and his boss, are intended to be slap-your-thighs hilarious but leave you cold. Keaton is hard to fault as the overbearing, over-the-top mum. She's in full flight here, and it's almost worth seeing Smother for her alone. And Shepard, too, is a comedic natural. But Tyler's character is a tad too one-dimensional, even for this kind of fluff. She's desperate to be a mother herself, and that's all that we really know about her. The upbeat Hollywood ending helps you to forgive the flaws, but Smother lacks a real plot to hook you in. There are those witty one-liners - peaks in the graph - but overall this comedy flat-lines.